1. Field of the Invention
The present invention relates to a vibrating element, and more particularly, it relates to a vibrating element including a movable portion driven to vibrate at a prescribed resonance frequency.
2. Description of the Background Art
A vibrating element including a movable portion driven to vibrate at a prescribed resonance frequency is known in general, as disclosed in each of Japanese Patent Laying-Open No. 2004-242488, Japanese Patent No. 3806826, Japanese Patent Laying-Open No. 2002-277809, Japanese Patent Laying-Open No. 2007-151244 and Japanese Patent Laying-Open No. 2001-305471, for example.
The aforementioned Japanese Patent Laying-Open No. 2004-242488 discloses an electromagnetic actuator including a movable portion, first and second coils provided on the movable portion, a permanent magnet working a magnetic field on the first and second coils, two driving portions provided for the first and second coils respectively and capable of supplying driving currents and a detecting portion detecting counter electromotive force generated in the second coil. The electromagnetic actuator described in Japanese Patent Laying-Open No. 2004-242488 regularly supplies the driving current to the first coil, and detects the counter electromotive force generated in the second coil with the detecting portion. The electromagnetic actuator is so formed as to control the magnitudes of the driving currents supplied from the driving portions for rendering the amplitude of the movable portion constant on the basis of the detected counter electromotive force.
The aforementioned Japanese Patent No. 3806826 discloses a vibrating mirror scanner driving circuit including a vibrating mirror (movable portion), a coil, a driving portion and a voltage sampler (detecting portion). In this vibrating mirror scanner driving circuit, the driving portion applies an excitation pulse voltage to the coil at a frequency twice the resonance frequency of the vibrating mirror. However, the excitation pulse voltage is applied every half cycle of the vibrating mirror driven at the resonance frequency by reversing the polarity every cycle. At this time, a counter electromotive voltage resulting from vibration of the vibrating mirror is generated from the coil. The voltage sampler detects the counter electromotive voltage only in a period when the excitation pulse voltage applied every half cycle of the resonance frequency is not applied. The vibrating mirror scanner driving circuit described in Japanese Patent No. 3806826 is so formed as to decide a pulse rise time and a pulse fall time of the excitation pulse voltage on the basis of the detected counter electromotive voltage.
The aforementioned Japanese Patent Laying-Open No. 2002-277809 discloses a planar galvanomirror driving circuit including a planar galvanomirror, a pulse generating portion, a current setting portion and a counter electromotive force detecting portion. In this planar galvanomirror driving circuit, the pulse generating portion and the current set portion supply a pulse current matched with a target mirror rotation angle to the planar galvanomirror at a resonance frequency. When the planar galvanomirror vibrates due to this pulse current, counter electromotive force is generated in a coil of the planar galvanomirror. The counter electromotive force detecting portion is so formed as to detect this counter electromotive force. At this time, the planar galvanomirror performs pulse driving, and hence the first and second halves of a waveform detected by the counter electromotive force detecting portion have a pulse waveform and a counter electromotive force waveform respectively. The planar galvanomirror driving circuit described in Japanese Patent Laying-Open No. 2002-277809 is enabled to drive the planar galvanomirror by generating the pulse current in timing with a zero crossing point where positive and negative signs of the counter electromotive force waveform in the second half of the detective waveform are reversed.
The aforementioned Japanese Patent Laying-Open No. 2007-151244 discloses an electromagnetic actuator including a movable portion, a driving coil provided on the movable portion, a permanent magnet working a magnetic field on the driving coil, a driving pulse generation circuit and a synchronous timing detector detecting counter electromotive force generated in the driving coil while detecting a zero crossing position of the waveform of the detected counter electromotive force as synchronous timing. In this electromagnetic actuator, the waveforms of the counter electromotive force and a driving pulse supplied by the driving pulse generation circuit are mixed in a signal waveform detected by the synchronous timing detector. In the electromagnetic actuator described in Japanese Patent Laying-Open No. 2007-151244, the synchronous timing detector is enabled to extract only the counter electromotive force waveform by removing the driving pulse waveform mixed into the counter electromotive force waveform by a canceling pulse of an opposite phase synchronous with the driving pulse waveform and performing prescribed correction processing and removal of noise.
The aforementioned Japanese Patent Laying-Open No. 2001-305471 discloses an electromagnetic actuator including a movable portion, a coil mounted on the movable portion, a permanent magnet working a magnetic field on the coil, a driving portion supplying a pulse excitation current to the coil and a detecting portion detecting counter electromotive force generated in the coil. A signal obtained by adding up the pulse excitation current and the counter electromotive force generated in the coil is input in the detecting portion. In this electromagnetic actuator, the detecting portion can detect only the counter electromotive force in a non-supply time (OFF-state) of the excitation pulse current, and hence generates a voltage value for excitation timing by detecting a negative peak value of a detected voltage waveform, reversing the sign and multiplying the same by a prescribed coefficient. The driving portion is enabled to supply the pulse excitation current at a frequency matched with a resonance frequency by supplying the pulse excitation current at timing matched with the voltage value for the excitation timing. Thus, the electromagnetic actuator described in Japanese Patent Laying-Open No. 2001-305471 is enabled to acquire timing for resonantly driving the electromagnetic actuator while avoiding influence by the excitation current by detecting the negative peak value of the counter electromotive force in the non-supply time of the pulse excitation current supplied at the resonance frequency.
In the electromagnetic actuator described in the aforementioned Japanese Patent Laying-Open No. 2004-242488, however, two coils, i.e., the first coil regularly continuously supplying the driving current and the second coil for detecting the counter electromotive force must be provided, in order to detect the counter electromotive force generated due to the vibration of the movable portion. Further, the two driving portions are also required for supplying the driving currents to the two coils. Therefore, the structure of the electromagnetic actuator is disadvantageously complicated.
In the vibrating mirror scanner driving circuit described in the aforementioned Japanese Patent No. 3806826, the voltage sampler can detect the counter electromotive voltage only in the period where the excitation pulse voltage is not applied in each half cycle of the vibrating mirror driven at the resonance frequency, and hence a detectable period for the vibrational state of the vibrating mirror is conceivably disadvantageously short.
In the planar galvanomirror driving circuit described in the aforementioned Japanese Patent Laying-Open No. 2002-277809, the counter electromotive force waveform can be acquired only in the second half of the waveform detected by the counter electromotive force detecting portion (second half of the resonantly driven vibration), and hence a detectable period for the vibrational state of the planar galvanomirror is disadvantageously short.
In the electromagnetic actuator described in the aforementioned Japanese Patent Laying-Open No. 2007-151244, waveform processing circuits such as a noise removing circuit and a waveform correction circuit are required in order to extract only the counter electromotive force waveform, and hence the structure of the electromagnetic actuator for detecting the vibrational state of the movable portion is disadvantageously complicated.
In the electromagnetic actuator described in the aforementioned Japanese Patent Laying-Open No. 2001-305471, the vibrational state of the movable portion can be detected only in the non-supply time of the pulse excitation current supplied at the resonance frequency, and hence a detectable period for the vibrational state of the vibrating mirror is conceivably disadvantageously short.